Gibbs' attorney, Phil Stackhouse, acknowledged in his opening statement that Gibbs had taken fingers off the three victims and kept them as war trophies.
A prosecutor, Capt. Dan Mazzone, told the jurors at this base south of Seattle that this wouldn't be a case in which they would have to second-guess difficult combat decisions.
"This case is the exact opposite: It is about premeditated murder," Mazzone said.
Of the five soldiers charged as part of the so-called "kill team" within the platoon, three have pleaded guilty and agreed to testify against Gibbs.
Gibbs joined the unit in what was then known as the 5th Stryker Brigade in Kandahar province in late 2009. He soon began telling others how easy it would be to kill civilians, Mazzone said.
Stackhouse sought to lay the blame for any unjustified killings with Gibbs' comrades. When Gibbs came to the unit, hash smoking was already rampant, Stackhouse said. Gibbs did talk frequently of previous shootings he'd been involved in - including one in Iraq, when Gibbs fired on a car that refused to stop at a checkpoint, only to later learn that the vehicle was carrying an innocent Iraqi family.
The others may have misinterpreted Gibbs' stories, Stackhouse suggested.
"On hash-filled nights, under a cloud of intoxication . . . they'd talk about these things," he said.
Gibbs is accused of a wide range of misconduct, from providing a grenade used in January 2010 to kill the first victim, an unarmed farmer in a field in Kandahar province, to directly shooting or tossing grenades at the next two in February and May of that year. One co-defendant, then-Cpl. Jeremy Morlock of Wasilla, Alaska, said that he or Gibbs enlisted one other soldier to participate in each of the three killings.
Asked why he had taken part in the killings, Morlock, the first witness, testified yesterday that the unit had trained to be deployed to Iraq, and soldiers were frustrated that their orders were changed to Afghanistan. They wanted action and firefights; instead they got meetings, Morlock said.
"It was a lot of meet-and-greets, shaking hands," he said.
Prosecutors say Gibbs also led a group of others in assaulting a soldier who reported drug use in the unit. That soldier, Pfc. Justin Stoner, ultimately prompted the war crimes investigation by telling investigators who were looking into his beating that members of his platoon had engaged in unjustified kills.
Gibbs' trial is expected to last at least until Friday. The verdicts need not be unanimous; four out of five jurors must agree to convict him.